U.S. patent number 6,477,362 [Application Number 08/844,883] was granted by the patent office on 2002-11-05 for systems and methods for providing information to emergency service centers.
This patent grant is currently assigned to Ericsson Inc.. Invention is credited to Gregory E. Bottomley, James Ragsdale, Alex K. Raith.
United States Patent |
6,477,362 |
Raith , et al. |
November 5, 2002 |
Systems and methods for providing information to emergency service
centers
Abstract
Emergency call handling may, in the near future, require
terminal unit location information to be provided to emergency
service centers. Exemplary embodiments of the present invention
provide techniques which pass the mobile unit's phone number along
to an appropriate emergency service centers in addition to location
information. This information can be made available to an adjunct
monitoring system by either changing the mobile station identity
used to package (Layer 2) an access attempt or by commanding a
mobile or base station to explicitly transmit the mobile unit's
dialable number during an emergency access so that the adjunct
system can read and forward this number.
Inventors: |
Raith; Alex K. (Durham, NC),
Bottomley; Gregory E. (Cary, NC), Ragsdale; James
(Raleigh, NC) |
Assignee: |
Ericsson Inc. (Research
Triangle Park, NC)
|
Family
ID: |
25293866 |
Appl.
No.: |
08/844,883 |
Filed: |
April 22, 1997 |
Current U.S.
Class: |
455/404.1;
455/521; 455/456.5 |
Current CPC
Class: |
H04W
4/90 (20180201); H04W 76/50 (20180201) |
Current International
Class: |
H04Q
7/38 (20060101); H04Q 007/22 () |
Field of
Search: |
;455/404,521,527,517,524,507,422,561,456,432,433 ;379/37,45,46
;342/457,357,354.01 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
International Search Report re PCT/US98/06497 Date of mailing of
search: Oct. 16, 1998..
|
Primary Examiner: Kincaid; Lester G.
Attorney, Agent or Firm: Myers Bigel Sibley &
Sajovec
Claims
What is claimed is:
1. A method for handling an emergency call in a radiocommunication
system, comprising the steps of: identifying, in a mobile unit, a
call as one of an emergency call and a non-emergency call;
selecting a first mobile unit identifier if said call is an
emergency call; selecting a second mobile unit identifier if said
call is a non-emergency call; and transmitting a message from said
mobile unit to said system using said selected mobile unit
identifier.
2. The method of claim 1, wherein said first mobile unit identifier
is a mobile identification number (MIN).
3. The method of claim 1, wherein said first mobile unit identifier
is an activating mobile identification number (AMIN).
4. The method of claim 1, wherein said second mobile unit
identifier is a temporary mobile station identifier (TMSI).
5. The method of claim 1, wherein said first mobile unit identifier
includes a dialable number associated with a mobile unit.
6. The method of claim 1 further comprising the steps of:
receiving, at an adjunct system, said selected mobile unit
identifier in signaling data associated with an emergency call from
said mobile unit; determining a position of said mobile unit; and
forwarding said position and said selected mobile unit identifier
from said adjunct system to an emergency service center.
7. The method of claim 6, further comprising the step of forwarding
to said emergency service center, without routing through the radio
communication system, said selected mobile unit identifier.
8. A method for handling an emergency call in a radiocommunication
system, comprising the steps of: identifying, in a mobile unit, a
call as one of an emergency call and a non-emergency call;
retrieving a stored dialable number associated with said mobile
unit if said call is an emergency call; retrieving a temporary
mobile station identifier (TMSI) if said call is a non-emergency
call; and selectively transmitting a message to said system
including said dialable number or said TMSI.
9. The method of claim 8, further comprising the steps of:
inputting, by a user of said mobile unit, said dialable number to
said mobile unit; and storing said dialable number.
10. The method of claim 8, further comprising the steps of:
transmitting, over an air interface, said dialable number to said
mobile unit; and storing said dialable number.
11. A remote station comprising: means for identifying a call as
one of an emergency call and a non-emergency call; means for
selecting a first mobile unit identifier if said call is an
emergency call; and means for selecting a second mobile unit
identifier if said call is a non-emergency call; and means for
transmitting a message from said mobile unit using said selected
mobile unit identifier.
Description
BACKGROUND
Applicants' invention relates generally to radiocommunication
systems, e.g., cellular or satellite systems and, more
particularly, to techniques for supporting and enhancing emergency
calling procedures in such systems.
The growth of commercial radiocommunications and, in particular,
the explosive growth of cellular radiotelephone systems have
changed the ways in which people communicate. One survey indicates
that about 80% of the people who purchase mobile communication
units and service subscriptions do so to enhance their personal
security. Presumably, many of these subscribers would expect to use
their mobile units to aid them in urgent situations, e.g., when
their vehicle has become disabled or in an emergency situation
requiring rapid medical and/or police response. In these
circumstances it would be desirable that the radiocommunication
system be able to independently determine a location of the mobile
unit, particularly in the case where the subscriber does not know
his or her precise location. Moreover, it is expected that the FCC
will soon require that network operators forward the position of an
emergency caller to the emergency service provider.
There are many techniques available to generate mobile unit
location information. In a first category, the mobile unit could
estimate its own position and send a message with its coordinates
when placing an emergency call. This could be accomplished by, for
example, providing the mobile unit with a Global Positioning System
(GPS) receiver that receives location information from the GPS
satellite network. The mobile unit can then transmit this
information to the system, which would then forward it to the
emergency service provider. This requires, however, significant
modification of existing mobile units to include GPS receivers, as
well as additional signalling between the mobile units and base
stations.
Alternatively, the base stations which transmit signals to, and
receive signals from, the mobile units could be used to determine
the mobile unit's location. Various techniques, including
attenuation of a mobile unit's signal, angle-of-arrival, and
difference between the time-of-arrival (TDOA) of a mobile unit's
signal at different base stations, have been suggested for usage in
providing mobile unit location information. See, for example, the
article entitled "Time Difference of Arrival Technology for
Locating Narrowband Cellular Signals" by Louis A. Stilp, SPIE Vol.
2602, pp. 134-144. These solutions also have their drawbacks
including the need to modify the many existing base stations, e.g.,
to provide array antennas to support angle-of-arrival techniques or
to synchronize base station transmissions to support TDOA
techniques.
A third category of strategies for locating mobile units in
radiocommunication systems involves the provision of an adjunct
system, i.e., a system which may be completely independent of the
radiocommunication system or which may share various components
(e.g., an antenna) with the radiocommunication system but which
processes signals separately therefrom. This may be advantageous,
for example, as an expedient solution to providing mobile unit
location without modifying the large number of existing base
stations in a system. For example, consider the equipment
illustrated in FIG. 1 wherein the adjunct scanning units are not
co-located with the base stations of radiocommunication system.
Therein, a base station 1 supports radiocommunication within cell 2
and, in particular with mobile unit 3. An adjunct system, partially
shown by way of scanning units 4, 5 and 6, monitors accesses to the
system by mobile unit 3. When mobile unit 3 makes an emergency
access, adjunct units 4, 5 and 6 can detect this emergency access
by, for example, the presence of a set emergency flag in an
origination message or based upon the dialed number. The adjunct
units can then use the mobile unit's transmissions on either a
control channel or a traffic channel to provide information to a
location processing center 7. The location processing center then
uses the information provided by the various adjunct units to, for
example, triangulate the position of mobile unit 3 and report this
position to an emergency service center 8. More details regarding
exemplary usages of adjunct systems can be found in U.S. Patent No.
5,327,144 to Stilp et al., entitled "Cellular Telephone Location
System", the disclosure of which is incorporated here by
reference.
However, one problem associated with the use of adjunct systems
involves the desirability of the emergency center mapping the
location of a mobile unit provided by the adjunct system with the
emergency call received from the radiocommunication system.
Consider this issue in the context of systems operating in
accordance with IS-136, which has three types of mobile
identifiers. The mobile identification number (MIN) is the same
identifier as used in the older analog AMPS system and is a binary
representation of the mobile station's phone number, which is also
referred to as the directory Number (DN). Given the need for global
mobility, however, the differences between these and other existing
techniques for identifying mobile units need to be reconciled.
This, among other reasons, lead to the development of the
International Mobile Station Identifier (IMSI), which is a decimal
identifier number having a maximum of 15 decimal digits. Although
IMSI is not a dialable number, it does solve the problem of
international roaming and is transmitted over the air interface as
a mobile station identification (MSID) encoded to 50 bits. Due to
the length of IMSI, however, a single page message transmitted by
the radiocommunication system can carry three pages to mobiles
using MIN but only one page using IMSI. Thus, using IMSI reduces
the paging capacity (pages per time unit) per control channel.
In order to overcome this problem and further increase the paging
capacity compared with the MIN, but still provide the capacity for
international roaming, the Temporary Mobile Station Identifier
(TMSI) was introduced. In IS-136 the length of TMSI is 20 or 24
bits which results in four or five pages per paging message,
respectively. The TMSI is assigned to a mobile station in a TMSI
assignment procedure after which the mobile station can be reached
by the cellular system using the TMSI. When the mobile unit travels
to a "new" system, the mobile unit is reassigned a new TMSI
controlled by the "new" system. In addition to being used to
contact a mobile unit, the same identity type is typically used
when the mobile station contacts (i.e., makes an access attempt
with) the cellular system. Thus, for mobile units having an
assigned (also referred to as "active") TMSI, this may
conventionally be the identifier which is used in access messaging
between the mobile unit and the system.
The radiocommunication system has the capability to translate these
identifiers into the mobile unit's dialable number and provide both
the emergency call and the dialable number to the emergency service
center. However, usage of IMSI and TMSI poses a problem for an
adjunct positioning system. Specifically, the "phone number" of the
mobile unit 3 is typically not present in the signalling which is
monitored by the adjunct scanning units 4, 5 and 6 and the adjunct
system cannot keep track of the various TMSIs assigned by the
radiocommunication system. Thus, although the adjunct system can
estimate the position of the mobile unit, e.g., as described in
U.S. Pat. No. 5,327,144 to Stilp et al., the adjunct system can not
forward the "phone number" to the application, e.g., emergency
service center 8. Thus, emergency service center 8 will have
difficulty mapping the position information received from the
adjunct system with the emergency call received from the
radiocommunication system. Accordingly, it would be desirable to
provide techniques for the emergency service center to receive
information regarding the phone number associated with a mobile
unit making an emergency access to a radiocommunication system.
SUMMARY
According to exemplary embodiments of the present invention, these
drawbacks and limitations of handling emergency calls are overcome.
For example, upon recognizing that an emergency call is to be made,
a mobile unit can ignore typical access rules and use its MIN as
part of its system access messaging. In this way, the adjunct
system can acquire and forward this information to the appropriate
emergency service center. Alternatively, or in addition thereto,
the system can use the MIN to address messaging in the downlink,
which could also be monitored by the adjunct system.
According to another exemplary embodiment, the mobile unit may,
upon recognition of an emergency call, use its predefined mobile
station identity type for addressing during system access, but
include its dialable number as part of the access payload.
Similarly, the system (i.e., the base station) can transmit that
mobile unit's dialable number as an address of a response to an
emergency access attempt. In either case, the adjunct system can
read this information and forward same to the emergency service
center.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of Applicants' invention will be
understood by reading this description in conjunction with the
drawings, in which:
FIG. 1 is a diagram of an exemplary cellular radio telephone system
having an adjunct monitoring system for providing mobile unit
location information to an emergency service center in which the
present invention may be applied;
FIG. 2 illustrates an exemplary base station and mobile unit which
may operate in accordance with the present invention;
FIG. 3 is a portion of a chart illustrating RACH fields according
to IS-136;
FIG. 4 is a flow chart illustrating a first exemplary embodiment of
the present invention; and
FIG. 5 is a flow chart illustrating a second exemplary embodiment
of the present invention.
FIG. 6 is a flow chart illustrating a third exemplary embodiment of
the present invention.
DETAILED DESCRIPTION
The following description is scripted in terms of a cellular
radiotelephone system, but it will be understood that Applicants'
invention is not limited to that environment and may be used in
other types of wireless systems, e.g., systems which provide
radiocommunication service using satellites, voice-trunked systems
such as Land Mobile Radio (LMR) or Special Mobile Radio (SMR)
systems, etc. Also, while the exemplary embodiments described below
are provided in the context of Time Division Multiple Access (TDMA)
communication systems, it will be understood by those skilled in
the art that the present invention may be applied to systems using
any access methodology, e.g,. Frequency Division Multiple Access
(FDMA), Code Division Multiple Access (CDMA) and hybrids of FDMA,
TDMA and/or CDMA.
Consider, solely for the purposes of example, the prevalent digital
cellular radiotelephone system in North America known as the
digital advanced mobile phone service (D-AMPS), some of the
characteristics of which are specified in the interim standard
IS-54B, "Dual-Mode Mobile Station-Base Station Compatibility
Standard", published by the Electronic Industries Association and
Telecommunications Industry association (EIA/TIA). Because of a
large existing consumer base of equipment operating only in the
analog domain with frequency-division multiple access (FDMA),
IS-54B is a dual-mode (analog and digital) standard, providing for
analog compatibility in tandem with digital communication
capability. For example, the IS-54B standard provides for both FDMA
analog voice channels (AVCs) and TDMA digital traffic channels
(DTCs), and the system operator can dynamically replace one type
with the other to accommodate fluctuating traffic patterns among
analog and digital users. The AVCs and DTCs are implemented by
frequency modulating radio carrier signals, which have frequencies
near 800 megahertz (MHz) such that each radio channel has a
spectral width of 30 kilohertz (KHz).
The IS-54-B standard also provides for a number of analog control
channels (ACC) on which system accesses can be initiated and system
overhead information can be communicated to the mobile units. A
subsequent standard, referred to as IS136, adds specifications for
digital control channels (DCCs), which standard is incorporated
here by reference.
In a TDMA cellular radiotelephone system, each radio channel is
divided into a series of time slots, each of which contains a burst
of information from a data source, e.g., a digitally encoded
portion of a voice conversation. The time slots are grouped into
successive TDMA frames having a predetermined duration. According
to IS-54B and IS-136, each TDMA frame consists of six consecutive
time slots and has a duration of 40 milliseconds (msec). Thus, each
frame can carry from one to six channels (e.g., one to six radio
connections), which may be a mixture of DTCs and DCCs used to
convey information between a base station and a mobile station.
FIG. 2 represents a block diagram of an exemplary cellular mobile
radiotelephone system, including an exemplary base station 110 and
mobile unit 120. The base station includes a control and processing
unit 130 which is connected to the MSC 140 which in turn is
connected to the PSTN (not shown). General aspects of such cellular
radiotelephone systems are known in the art, as described by U.S.
Pat. No. 5,175,867 to Wejke et al., entitled "Neighbor-Assisted
Handoff in a Cellular Communication System," and U.S. patent
application Ser. No. 07/967,027 entitled "Multi-Mode Signal
Processing," which was filed on Oct. 27, 1992, both of which are
incorporated in this application by reference.
The base station 110 handles a plurality of traffic channels
through a traffic channel transceiver 150, which is controlled by
the control and processing unit 130. Also, each base station
includes a control channel transceiver 160, which may be capable of
handling more than one control channel. The control channel
transceiver 160 is controlled by the control and processing unit
130. The control channel transceiver 160 broadcasts control
information over the control channel of the base station or cell to
mobiles locked to that control channel. It will be understood that
the transceivers 150 and 160 can be implemented as a single device,
like the traffic and control transceiver 170 in the mobile station,
for use with control channels and traffic channels that share the
same radio carrier frequency.
After an idle mobile unit 120 has located a control channel, e.g.,
by using digital control channel location information found on a
traffic channel, it can then read the control information
transmitted on that control channel, e.g., paging messages, using
its traffic and control channel transceiver 170. For more detailed
information relating to techniques for locating digital control
channels, the reader is referred to U.S. patent application Ser.
No. 08/331,711 entitled "Method and Apparatus for Locating a
Digital Control Channel in a Radiocommunication System", filed on
Oct. 31, 1994, the disclosure of which is incorporated here by
reference. When a connection between the mobile station 120 and the
system is desired, the transceiver 170 will tune to a traffic
channel assigned thereto by the system.
Once the mobile unit has found a control channel which satisfies a
minimum set of rules, e.g., the mobiles must be able to receive the
channel above a minimum received signal strength, the mobile may
further evaluate this control channel with regard to certain system
preferences stored in the mobile unit. For example, if the cell is
barred (as described in IS-136), or the cellular operator is not
the preferred operator (using the System Operator Code in IS-136),
the mobile unit may then try to find another control channel.
If the data broadcast by the cellular system on the control channel
(this part of the DCC is often referred as to the Broadcast Control
Channel or BCCH) satisfies the preferences stored in the mobile
unit, the mobile unit will listen or lock to this control channel
to listen for paging messages and/or transmit call origination
messages. At the same time, however, the mobile unit prepares for
potential cell reselection since the mobile may be traveling and
leaving the coverage area of the first selected control channel.
Many known techniques exist for informing a mobile unit where
(e.g., using one or more of frequency, time, and code) the
neighboring control channels can be found in order for mobile units
to test and compare these candidates with the current control
channel to find the best control channel to serve the mobile unit
given its current position. See, for example, U.S. Pat. No.
5,353,332 to Raith and Muller, entitled "Method and Apparatus for
Communication Control in a Radiotelephone System" or U.S. Pat. No.
5,499,386, entitled "Best Server Selection in Layered Cellular
Radio System" to Karlsson, the disclosures of which are
incorporated here by reference.
As discussed above, it may be important for the emergency service
center 8 to receive the phone number of the mobile unit which
placed an emergency call. For example, the original call may be
dropped, so that having access to the phone number makes allows the
emergency service center to call this particular mobile unit to
re-establish the communication link. Additionally, the phone number
may be of importance in documenting the emergency request. Further,
if the emergency service center does not receive the phone number
from the adjunct system, it may be difficult to map the position
information received from the adjunct system with the emergency
call received from the cellular system.
When a mobile unit makes an access attempt to establish a
connection with a radiocommunication system, it does so by sending
messages on an uplink access channel or control channel. In systems
specified by IS-136, the uplink control channel is referred to as
the Random Access CHannel (RACH). A portion of the field
definitions for the Layer 2 RACH protocol is reproduced as FIG. 3.
For this particular discussion, only the identity type (IDT) and
mobile station identity (MSID) fields are of interest and described
here. In these fields, it can be seen that any one of the 20-bit
TMSI, the 24-bit TMSI, the 34-bit MIN or the 50-bit IMSI can be
sent by the mobile unit when making a system access on the
RACH.
In fact, the mobile unit will transmit its TMSI value in the MSID
field if it has a valid (as defined in IS-136 Section 8.1.2.2)
TMSI. If the mobile unit only has an IMSI, then it will use the
IMSI as its MSID. Similarly, if the mobile unit only has a MIN,
then it will use the MIN as its MSID. If the mobile unit has both
an IMSI and a MIN, then the selection of one of these identifiers
is made in accordance with rules which are also defined in IS-136.
Significantly, following the rules defined by the standard leads to
only a relatively few mobile units supplying their MIN as part of
an access burst. Thus, the adjunct stations 4, 5 and 6 will receive
the TMSI or IMSI in many uplink bursts.
In these cases, the adjunct stations can, according to one
exemplary embodiment of the present invention, forward this TMSI
information to the emergency service center 8, along with the
location information generated by location processing center 7 and,
optionally, an indication that a permanent mobile station
identification (PMSID) is not available. Although not usable by the
emergency service center to call the mobile unit back, the TMSI can
be stored by the emergency service center 8 for later usage, e.g.,
by the authorities in conjunction with information available in the
cellular radiocommunication system to later identify the mobile
unit by tracing the DN from the TMSI and the time of the call. If
the IMSI is used, the time is not needed since the IMSI is only
changed when the subscription record in the home system is changed
which is typically is not a frequent event.
Alternatively, it may be desirable to ensure that the emergency
service center 8 actually receive the mobile unit 3's phone number.
According to another exemplary embodiment of the present invention,
depicted by way of the flow chart of FIG. 4, the mobile unit will
use its MIN instead of TMSI or IMSI when it detects that an
emergency call is being placed. Therein, at step 400, the mobile
unit evaluates a call being placed to determine if it is an
emergency call. This can be accomplished, for example, as described
in U.S. patent application Ser. No. 08/843,752, entitled "Systems
and Methods for Identifying Emergency Calls in Radiocommunication
Systems, filed on Apr. 22, 1997, the disclosure of which is
incorporated here by reference.
If the call is not an emergency call, then the flow proceeds to
block 410, wherein the "normal" identity type is used by the mobile
unit to perform the access attempt. For example, assuming that an
IS-136 conformant mobile unit has a valid TMSI, then that value
would be used in the RACH messages transmitted by the mobile unit.
If the call is an emergency call, then the flow instead proceeds to
block 420, where the mobile station selects an identity type (if
any) which is equivalent to its dialed number. Using the previous
example, the IS-136 mobile unit would use its MIN in transmitted
RACH messages instead of its valid TMSI or IMSI. In this way, the
adjunct scanning stations will receive the mobile unit's MIN and
can forward this information to emergency service center 8, along
with the location information generated by the location processing
center 7.
According to another exemplary embodiment of the present invention,
the mobile unit uses an identity according to the system specified
rules, e.g., using MIN, IMSI or TMSI in the above-described fields
in Layer2, but also includes the mobile unit's dialable number (DN)
as part of the access, e.g., as part of a Layer3 message. The
mobile unit can store the DN, which may be input into the unit by
the user. Alternatively, for example in units operating in
accordance with IS-136, the DN can be downloaded to the phone as
part of the over-the-air interface activation service (OATS).
Moreover, when the mobile unit is purchased it may not contain an
identity (e.g., MIN, IMSI). For IS-136, the mobile unit makes an
access using the Activating MIN (AMIN) which is constructed from
the Electronic Serial Number (ESN) for this special access. Thus,
if the user needs to make an emergency call at this point in time,
the mobile unit would use the AMIN as the PMSID in the RACH field
and make the emergency access as described above.
Otherwise, if the user makes a "normal" initial access to the
system using the AMIN, the system may now download (among other
things) this mobile unit's identity (e.g., MIN and/or IMSI). Note
that there may be multiple instances of identities each linked to a
separate subscription. For example, different family members may
use the same mobile unit, wherein each user activates a different
subscription. Alternatively, a single user may have multiple
subscriptions because he or she may want to activate on two systems
to avoid roaming charges. In any event, for each logical identity
(which for IS-136 can the MIN and/or IMSI), the download message
may contain the associated DN. Thus, the user can have the DN
displayed for the current subscription and this DN can also be
transmitted to the system during emergency calls.
According to another exemplary embodiment, the adjunct system can
acquire the DN by listening to the downlink control channel. For
example, the system may respond to the mobile unit using its MIN
and the adjunct system can read this information on the DCC.
However, this assumes that the mobile unit is listening to both its
MIN and the identifier type used when making the access, e.g. TMSI,
as an address. If the particular system protocol does not mandate
that the mobile unit listen to both identity types, the system can
use the same identity type as used by the mobile unit when sending
a response to the mobile and include the DN as part of the payload
in the message.
These exemplary embodiments involving the explicit transmission of
the DN in Layer 3 are summarized by way of the flow chart of FIG.
5, which technique is generic to mobile unit and base station
operation (i.e., uplink or downlink). Therein, at block 500, the
call is identified as emergency or non-emergency. If the call is a
non-emergency call then the message, e.g., a RACH or ARCH message,
is processed in accordance with the appropriate standard and system
rules at block 510. Otherwise, if the call is an emergency call,
then the dialable number is included in a message (step 520) which
is transmitted at block 530 using the standard or system specified
mobile station identifier for Layer 2 addressing.
In accordance with another exemplary embodiment, as summarized by
way of the flow chart of FIG. 6, a method of forwarding a mobile
unit position and a mobile unit identity for a mobile unit making
an emergency call in a radio communication system is provided with
reference to an adjunct system. In step 600, the adjunct system
receives the mobile unit identity in signaling data associated with
an emergency call from the mobile unit. The position of the mobile
unit is then determined in step 610. Subsequently in step 620, the
position and mobile unit identity are forwarded from the adjunct
system to an emergency service center. In accordance with yet
another embodiment of the invention, the forwarding of the position
and mobile unit identity in step 620 is accomplished without
routing the information through the radio communication system.
It is, of course, possible to embody the invention in specific
forms other than those described above without departing from the
spirit of the invention. Thus, the embodiments described above are
merely illustrative and should not be considered restrictive in any
way. The scope of the invention is determined by the following
claims, rather than the preceding description, and all variations
and equivalents which fall within the scope of the claims are
intended to be embraced therein.
* * * * *